This invention relates to generally to agricultural combines and specifically to an improved chaffer/sieve for such combines.
Agricultural combines are widely available machines which enormously speed the processes of harvesting, threshing and cleaning of all types of grains. By minimizing the labor required for harvesting, combines have contributed to the dramatic increase in availability and decrease in price of grains.
The combine machine traverses the field of grain in swathes which cover the area of the ripened crop. As it travels, the combine brings grain into its forward end and feeds it to a separating apparatus or thresher which threshes the grain, separating grain and grain heads from stalks, straw, dirt and other undesirable materials. An example of an axial flow rotor for threshing of the grain may be seen in U.S. Pat. No. 5,125,871, issued Jun. 30, 1992, to the same inventor as the present application. The present invention concerns the succeeding processing stage: the chaffing of the grain.
After passing through the threshing stage, the grain is theoretically perfectly threshed. In reality, however, while the separating apparatus is efficient, some chaff, unthreshed grain, other materials, stems, and/or straw remains intermixed with the grain and further steps of threshing, separating and cleaning are normally required.
The cleaning section of a conventional combine is located to receive grain and other material expelled from the separating apparatus. A typical cleaning section includes a chaffer and a sieve mounted so as to move back and forth reciprocally and a fan which produces a flow of air directed through the sieve and chaffer. The sieve is usually mounted below the chaffer, although it important to note that some combines have several layers of sieves and chaffers, or several in sequence. In theory, the chaffer blows the chaff and other xe2x80x9cmaterials other than grainxe2x80x9d (xe2x80x9cMOGxe2x80x9d) out of the stream of grain before the sieve sifts it. Reciprocation of the chaffer and sieve facilitates arrangement of the grain and other materials into a crop layer or mat on top of the chaffer. Separation of the crop material is largely facilitated by the air from the fan flowing upwardly through the passages between the louvered sieve and chaffer. Prior art chaffers/sieves include a series of adjacent louvers. A series of transverse elongated openings or passages are defined between the adjacent louvers to grade the material by density and size. Smaller, denser kernels of grain are allowed to fall through the openings despite the airflow upwards therefrom, after which they fall through the sieve mounted below the chaffer, whereas larger pieces of materials are blown or vibrated rearward in the airflow and off of the chaffer and sieve. The light material blown off the chaffer is discharged from the combine entirely, while heavier unthreshed heads of the crop still having grain is too heavy to blow and thus is moved off of the rear of the sieve, from where it is returned by the tailings system to the separating apparatus for rethreshing. Finally, there is larger MOG which is carried over the end of the chaffer and falls or blows away from there.
Thus four categories of material are created: first, the grain, which falls through the chaffer/sieve for storage, second unthreshed material which is sent back for rethreshing, and third chaff, which is blown entirely clear. Fourth, the larger material other than grain is carried off the end of the rethreshing louvers of the chaffer. To allow use of a single chaffer for grain crops of different sizes, the louvers may be adjusted in rotation, thus altering the spacing between the louvers and the characteristics of the air-flow/air-blast through them.
The proper opening between the louvers is necessary for efficient operation of the combine""s chaffer. If the openings are too large, straw and other material ends up falling between them with the grain, contaminating the grain. On the other hand, if the louvers are adjusted to have openings which are too small, the individual grain requires a longer average time before finding a hole of sufficient size to pass through, thus causing a buildup of the grain, thus causing an unpredictable diminishment of the air flow, thus reducing both the speed and the efficiency of operation. Worse, some of the grain is carried off the back of the chaffer and if it falls through the louvers, is returned to the thresher unnecessarily, resulting in an excessive percentage of the grain being cracked, or if it is carried over the louvers ends up falling out the back of the combine and being lost. If the louvers are not evenly adjusted the grain may not receive uniform treatment, and in some areas, the MOG may fall through the chaffer while in others, even grain is blown away.
One particular issue is that the husk surrounding the grain may cling tightly to the grain, especially in a wheat crop, resulting in xe2x80x9cwhite capsxe2x80x9d: kernels slightly larger than the norm having husk still attached. Adjusting chaffers to use only size in a sifting or filtering apparatus to successfully reject the white caps while accepting the only slightly smaller grains which are fully threshed is a difficult process. The size difference between the chaffed and unchaffed grains can be minute: in wheat, the size difference may be as small as {fraction (5/1000)} of an inch.
An example of prior art that shows a commonly used louvered system is U.S. Pat. No. 4,511,466, issued Apr. 16, 1985 to Jones et al for xe2x80x9cChaffer Slatxe2x80x9d. This clearly shows that the grain flow must make a turn in flow direction in order to advance to the clean grain collection system, this turn may be anywhere from 90 degrees to almost 180 degrees, depending upon circumstances. The grain density is greater than that of the chaff, and the grain has more inertia than does the chaff, and this inertia must be overcome in making the turn. Also, in order for the grain to fall through a louver chaffer it must rely on gravity to drop between the louvers and penetrate the blast of air passing in the exact opposite direction. As can be easily appreciated there is a conflict at this point: a powerful blast of air is needed to float the chaff above the chaffer and out the back end of the combine, but the blast must not be so strong as to prevent the grain (which is being driven backwards across the chaffer) from making its turn and falling against that air blast through the louvers to the clean grain collection system. It is also worth noting that while the grain flow path pictured in FIG. 1 of the ""466 patent is depicted to closely follow the underside of each louver, in fact gravity and the reciprocating motion of the chaffer causes the grain to actually land upon the top side of the following louver. However, this contact with the topside of the following louver supports the grain and diminishes the effect of gravity in moving the grain downwards against the blast of air. In addition, the MOG tends to comprise a mixture which may include straight stalks of various lengths. With large numbers of such stalks continuously fluttering and twirling in the air blast, it is inevitable that some number of them randomly end up aligned parallel to the air blast. They can then fall with great ease straight into the air blast. The slats pictured by the ""466 patent are unlikely to catch and filter out such stalks as the slats are themselves aligned parallel to the airflow, and thus a certain percentage of stalks can simply fall straight through the chaffer to contaminate the grain. One final problem with such devices is that the reciprocating motion of the chaffer/sieve combination tends to xe2x80x9cstuffxe2x80x9d the lighter, less inertia driven material, (chaff, and other materials other than grain) into the slanted louver openings, contributing to the problem of fouling of the chaffer/sieve.
In such a louver or air foil chaffer system reliance for filtration is on the size of the openings, but in any given crop, the grain varies in size by as much as 100%. The openings of chaffers and sieves must be set wide enough to allow the largest individual grains of the crop to pass through. The opening is then wider than necessary for the smaller grains of the same crop. Any of the smaller grains that have attached husks (xe2x80x9cwhite capsxe2x80x9d) will pass through and contaminate the clean grain in the collection system. However, it is obvious that as the louvers are adjusted, the angle of the air blast is altered, the speed of the air blast is changed, the amount of support offered to the grains as they slide down the louvers is altered, and numerous other changes occur.
To illustrate the complexity of the mechanics involved, consider the case in which the louvers are narrowed from a fairly wide open configuration which was previously selected to allow a relatively large grained crop to pass there through. The narrowing of the louvers does allow them to function as screens or filters for a smaller size of crop. However, the smaller openings result in an air blast which is potentially more powerful, despite the fact that a smaller and lighter grain must now fight it""s way downwards against this blast. The louvers"" relatively flat angle means that the louver""s top surfaces offer to the smaller grains a greater degree of support, thus reducing the pull of gravity to overcome the air blast. The fan speed must thus be adjusted to attempt to compensate not only for the smaller crop but also for the unpredictable effects of the louvers on that crop. And the new lower angle of the air blast will tend to move the mat of grain and chaff backwards faster.
In systems commercially available, the construction of the chaffer is extremely light: thin metal louvers, supports of light construction, and moving parts having fairly generous tolerances. In addition linkages necessary to actuate the multiple slats must run from the back of the chaffer (where the operator may have access) to the front. The combined effect is to produce an uncertain control response. The loose linkages, multiplied over the length of the chaffer, may result in the louver adjustment at the front end being very different from the louver adjustment at the back end, where the operator can easily see it. Individual slats may be warped by fatigue or bent by MOG falling onto them from the separator. In some commercially available systems, the length of the chaffer is divided up into multiple zones, each having a separate control system, in an attempt to deal with these problems.
The sieve below the chaffer also has unpredictable effects on the chaffer""s efficiency and capacity. When filtering small seeds the angle of the louver is set as low as possible to allow the small seeds to pass into the clean grain collection system and prevent even slightly larger material other than grain from contaminating the collected clean grain. But the resulting restriction by the sieve of the air flow upwards to the chaffer starves the chaffer of needed air to function at a high capacity. To prevent overloading of the air starved chaffer, the operator must in turn slow the ground speed of the combine (thus decreasing the intake rate of the crop) or increase the speed of the cleaning fan to supply adequate air to the chaffer. Failure to do either will result in an overload condition on the top of the chaffer as is plugs with a mat of crop material. But increasing the fan speed, as discussed elsewhere, results in an undesirable loss of grain and also undesirable rethreshing of grain. Reducing ground speed and the rate of crop intake means that harvesting requires more time, which not only increases grain production cost but increases the chance that intervening events (time and weather, for example) may cause loss of a portion of the crop.
The reciprocating motion of the chaffer will also tend to move the mat of crop material (chaff, straw, stalks, and a percentage of grain) atop the chaffer rearwards out the discharge of the combine and waste whatever grain is mixed into the mat. If the operator attempts to prevent chaffer overload by increasing the fan output instead of reducing the ground speed of the combine, the sieve is over-driven with air and the grain is hit with a blast of air strong enough to blow into the tailings return auger and is needlessly rethreshed. As mentioned elsewhere, rethreshing of clean grain results in cracking and adds to the incoming crop from the harvester. When high levels of clean grain is returned to the thresher the ground speed of the combine must be reduced to prevent overload of the separator.
Other examples of such prior art combine chaffers include U.S. Pat. No. 5,041,059 issued on Aug. 20, 1991, to Ricketts et al, for xe2x80x9cCleaning System for a Combinexe2x80x9d and U.S. Pat. No. 6,053,812 issued on Apr. 25, 2000, to Loewen et al for xe2x80x9cSieve Construction for a Combine Harvesterxe2x80x9d. In the ""059 patent, a series of openings 88 are designed to allow grain to fall through louvers 62. However, since the louvers 62 have a gap between them, xe2x80x9callowing clean grain to fall through the sievexe2x80x9d (column 7, lines 14,15), materials larger than openings 88 may penetrate the chaffer of the ""059 reference. Having gaps wich allow the xe2x80x9cclean grainxe2x80x9d to fall through the xe2x80x9csievexe2x80x9d (the chaffer, despite the difference in naming convention) is both a drawback of the ""059 patent and a distinction between that patent and the present invention.
A reference of interest is U.S. Pat. No. 5,176,574, issued on Jan. 5, 1993 to Matousek et al for xe2x80x9cCombine Cleaning Systemxe2x80x9d. In the ""574 patent, numerous one dimensional jets or passages in an xe2x80x9cair foilxe2x80x9d section of the chaffer themselves function as the holes of a screen. As shown in FIG. 5 (the representative diagram), the jets 88 are aligned in parallel rows. However, as stated in column 3, lines 7-9, and other places in the reference, the passages provide granular sizing or sorting capability. While it appears at first glance of FIG. 1 that there is a separate sieve section aft of the air foil section, FIG. 2 shows that the section extending rearwards of the air foil section is used for larger materials which are being sent back for rethreshing: this section of the chaffer overhangs return auger 52, which structure returns unthreshed materials to the threshing stage. This same point is made in column 3, lines 42-47, xe2x80x9c. . . materials passing through the slat section get recirculated to the threshing apparatus.xe2x80x9d It is worth commenting that if the xe2x80x9cairfoilsxe2x80x9d of this reference were to be interspersed among the slats, or vice-versa, the larger materials such as chaff, white caps or unthreshed heads of the grain plants, all requiring rethreshing, would not get rethreshed and would instead get mixed with the cleaned grain. It is also worth commenting that both the air foil/sieve holes and the gaps between the slats are located on the forward side of the troughs in which the airfoils sit, and that the airfoil openings 88 would continue to function as a sieve themselves no matter how the ""574 reference is rearranged, as that structure and purpose is repeatedly taught in the reference, as pointed out above.
In general, the goals of combine chaffer designs are to first, allow a high capacity chaffing rate, that is to allow a high flow rate of partially threshed materials into and through the chaffer. This is of importance because the chaffing rate tends to be limiting factor in combine operation speed: increasing the chaffing capacity rate allows an immediate increase in combine operation. Second the chaffer must work efficiently to separate the grain from the chaff. High capacity of operations means little if the market quality of the grain is degraded substantially by the presence of excess chaff. These two goals may conflict.
In functional terms, turning up the air blast allows faster operation of the chaffer, up to that point when the air blast merely causes grain to be blown out the back of the combine with the chaff. This in turn leads to the observation that two separate operations are occurring in the chaffer: one operation is that grain is being separated, allowed to fall through the sieve, and collected. The other operation is that chaff is being blown backwards over the sieve and eventually out the back of the combine. (A third operation, alluded to earlier, is that unthreshed heads of grain are being collected for rethreshing.)
Another more practical problem with known chaffer designs is that of access to the chaffers and/or sieves, as well as adjustment, replacement, and cleaning. The combine has evolved into a complex machine with attachments such as grain loss monitors, chaff spreaders and straw choppers located at or near the discharge opening of the combine. These extra attachments make access to the chaffer difficult and requiring extensive time consuming disassembly to remove the chaffer and sieve. Thus whenever the chaffer must be changed, cleaned, adjusted or for any other routine maintenance, a good deal of effort is involved. In fact, the chaffer is normally only accessed from the rear, and the weight of any material clogging the chaffer, plus the weight of the chaffer and frame, plus the fact of access to one end only, all conspire to make pulling or adjusting the chaffer/sieve a tedious and difficult two person operation.
The present invention uses a series of substantially-uninterrupted precision lateral horizontal air jets that focus the air blast, supplied by the cleaning fan, into a thin, high velocity layer of air which approximately parallels the faces of the screens, rather than being primarily emitted from the orifices of the screens.
It is one feature of the invention that the air blast is directed above the screens, and so in addition to not passing through the screens also does not pass directly across the face of the screens.
In another embodiment of the invention, the faces of the screens are divided into a series of steps or troughs, in which the riser of each step (which riser may also be regarded as the front side of each trough) has at least one of the series of lateral horizontal air jets. Grain supplied to the first riser is pushed rearward by the face of the riser and by the thin layer of high velocity air streaming through the air jet. The effect of gravity causes the grain to penetrate the thin air stream and fall on the screen of one of the step/troughs. The angle of the screen faces the approaching grain and is selected so as to favor grain penetration. The grain on the screen is normally entirely below the thin high velocity air blast. As the screen is not the source of the air blast the grain is able to enter the openings of the screen without ever directly facing a strong air blast.
It is thus one additional aspect of the present invention that the grain does not have to reverse direction as it must in the louver or air foil chaffer/sieve designs. Since the grain does not have to fall directly against the air blast, the fan speed can be increased without blowing the grain out with the chaff or into the tailings return system.
It is another aspect of the present invention that as the fan increases in speed, back pressure is created inside the plenum (the area beneath the air jet chaffer). The back pressure causes air to rise through the screens. However since the screens are fixed at an angle parallel to air streaming from the cleaning fan directly toward the air jets, and since the holes in the screens are not designed as air jets, the air exhausting through the screen holes is at a much lower velocity than that from the air jets. The velocity of the air exhausting through the screen holes is sufficient to prevent chaff and other light material such as dust from entering the clean grain collection system. Such light material will be driven by vibration and air flow over the next riser and as it falls to the next trough/step, it will pass the next air jet and be lofted away from the screens.
It is a further feature of the present invention that any grain that bounces off the surfaces between the screen holes moves by inertia rearward to the next riser and thus the next series screen holes, until it penetrates a screen hole.
It is a further feature of the present invention that the air blast need not be powerful enough to drive grain substantially rearward, as the xe2x80x9cstep and riserxe2x80x9d architecture of the present invention assists the grain""s rearward travel.
In another embodiment of the present invention, the functions of sieve and chaffer are combined on the chaffer by means of two different structures: air jets and chaffing screens.
In another embodiment of the present invention, the air jets are longitudinally constricted in cross section so as to increase the speed of air flow there through and thus increase the air blast created.
It is a further aspect of the present invention that screen hole size and shape may be selected without regard to a xe2x80x9cfilteringxe2x80x9d function by the screen, as such filtering occurs above the screen.
It is a further aspect of the present invention that the air jet openings are not needed or used for grain separation.
In another embodiment of the present invention that the chaffer on the combine may be changed on an element by element basis, rather than by changing the entire chaffer.
In another embodiment of the present invention, the air jet openings and screen hole openings may be of fixed size and configuration so as to eliminate the need for frustrating and error-prone adjustment of louver configurations of prior art systems.
It is a feature of the present invention that lower cost chaffers may be manufactured which allow exacting standards for production and provide precision operation.
It is another feature of the present invention that white caps may be caught with a high degree of efficiency without the need for precision sifting.
It is a feature of the present invention that low cost chaffers which do not require any adjustment may be used, each chaffer being optimized to one grain type.